FIG. 1 shows a conventional OLED device 100. OLED devices can be used as displays in various consumer electronic products, including cellular phones, cellular smart phones, personal organizers, pagers, advertising panel, touch screen displays, teleconferencing equipment, multimedia equipment, virtual reality products, and display kiosks.
The OLED device comprises a functional stack of one or more organic functional layers 110 between a transparent conductive layer 105 and a conductive layer 115. The functional stack is formed on a transparent substrate 101. The conductive layers can be patterned to form one or more cells or pixels on the substrate. Bond pads 150 are coupled to the cathodes and anodes to control the OLED pixels. In operation, charge carriers are injected through the cathodes and anodes for recombination in the functional layers. The recombination of the charge carriers causes the functional layer to emit visible radiation.
A cap 160, which forms a cavity 145 between it and the pixels, is mounted on the substrate. A sealant 187 is applied around the edges of the cap where it contacts the substrate. No pressure is applied on the cap, thus allowing the sealant to creep in between the cap and the substrate by capillary force and hermetically sealing the device. However, due to the gap G that exists between the cap and substrate, the sealing width W needs to be sufficiently wide to prevent oxygen and moisture from permeating through the sealant. Typically, the sealing width is about 1-2 mm with a gap of about 0.01-0.1 mm. Such a large sealing width results in inefficient use of chip area, limiting miniaturization of OLED devices.
As evidenced from the above discussion, it is desirable to provide improved encapsulation of OLED devices which reduces the sealing width, control the sealing gap G and provide a cavity to prevent mechanical damage of the active device layers.